This invention relates in general to digital photofinishing systems and more particularly to a digital photofinishing system selectively including film under exposure gamma, scene balance, contrast normalization, and sharpening digital image processing for alternative capture color photographic media.
Several problem areas need to be addressed when making color negative paper prints from color negative film images. The object of the process is to make a pleasing print from the film image. The first problem is to find the level of exposure necessary in a projection printer system to produce that pleasing print. In the simplest implementation of a process, one projects the color negative film image onto a photosensitive paper image receiver, processes the paper, and then repeats the process until a pleasing print has been obtained. In automated photo-finishing operations, a film scanner reads densities from the negative and passes the information to a computer algorithm that computes the appropriate exposure values so that a pleasing print can be obtained. At this point, the conventional photographic printing process ends. That is, if there are any remaining problems in a photographic image, no other simple processes are available to reduce the severity of the problem. Problems such as film under-exposure or over-exposure, inappropriate gamma for a particular scene, poor quality camera or printer lenses, low or high activity of film or paper processes, poor scene balance, and poor sharpness in the final image remain that we would like to correct or modify.
Methods and systems have been described for more than 10 years that are devoted to producing pictorial images on various media and devices from scenes captured on photographic film, via scanning to produce a digital image, image processing, and output rendering. Examples include the following.
Journal of Imaging Technology, Vol. 14, Number 3, June 1988, Firth et. al. describe systems that capture scenes on film, scan film to produce a digital image, digitally process the image, and output via a laser AgX printer.
U.S. Pat. No. 4,500,919, Schreiber discloses an image reproduction system that scans an image captured on film, displays the image on a video monitor, enables image processing, and finally output to an inked hardcopy.
U.S. Pat. No. 4,979,032 (Dec. 18, 1990, filing date: Dec. 27, 1988), Alessi et al. describe an apparatus, including a film scanner, a video monitor, image processing, and output, to produce various output visually matched to the image displayed on the monitor.
U.S. Pat. No. 5,267,030, issued Nov. 30, 1993, inventors Giorgianni et. al. describe method and means to transform images captured on film, via digitization on a film scanner, to a color metric or other space, with output onto a variety of media and devices. This document describes the improvements offered by digital image processing, including aesthetically pleasing modifications to the tone and color reproduction as well as sharpening.
U.S. Pat. No. 5,300,381, issued Apr. 5, 1994, inventors Buhr et. al. describe a pictorial imaging system that consists of capture on photographic film, film scanning to produce a digital image, image processing, and digital output.
U.S. Pat. No. 5,579,132, issued Nov. 26, 1996, inventor Takahashi describes an image processing system devoted to storing or producing images that have xe2x80x9csubstantially the same colorxe2x80x9d or additional xe2x80x9caesthetic color correctionxe2x80x9d versus the original scene, based on a variety of image processing transformations of the digitized image.
U.S. Pat. No. 5,608,542, issued Mar. 4, 1997, inventors Krahe et. al. describe a system that produces index prints based on scanning a film frame, image processing, and rendering.
U.S. Pat. No. 4,945,406, issued Jul. 31, 1990, inventor Cok, describes a system for achieving automatic color balancing of color images by transferring color pixel values from log exposure RGB color values into printing density values and generating color correction offset values utilizing a printing density based color correction method.
The KODAK 35 mm/24 mm color negative film format Index Printer, sold by Kodak, produces an index print (a matrix of small imagettes) reproduced from individual film image frames. The index print is produced by the photofinisher when the original print order is processed and is supplied to the customer as a convenient means of identifying image frames on the film (see: U.S. Pat. No. 5,608,542, above). The Kodak Index Printer uses image processing on the miniature images including:
digital image in film RGB printing density
applying a scene balance algorithm to balance the digital film printing density image
mapping the color negative digital image onto a color paper (EDGE-type) characteristic curve
digital sharpening
rendering using a CRT printer onto photographic paper
In the Index Printer, the above image processing: (1) is not applied to full frame images in a digital color printer; and (2) is not applied to high resolution images in a digital color printer, only low resolution images.
U.S. Pat. No. 5,134,573, issued Jul. 28, 1992, inventor Goodwin, discloses a method for increasing the range of values representing a color image which exhibit a linear response. The toe and/or shoulder regions of the film""s three density vs. log exposure tables are straightened using look up tables.
U.S. Pat. No. 5,012,333, issued Apr. 30, 1991, inventors Lee et al., discloses a dynamic range adjustment system for printing digital images based on visual photoreceptor adaption and human visual contrast sensitivity. The system adjusts the contrast of the low frequency component only of the image, preserving the high frequency component in its contrast.
All of these articles or patents describe, in one form or another, processes for obtaining more pleasing prints from a film image capture than the conventional optical process. There is thus a need for a solution to these problems, which can be incorporated into a digital photofinishing system.
While it is straight-forward to produce high-quality images from high-quality media capture through standard optical-printing photo-finishing on high-quality color photographic paper using high-quality chemical processing and printing equipment that is properly run, it would be beneficial to produce high-quality images from capture media that would not produce such results using the same optical printing photo-finishing path. Such light-sensitive media might be lower in cost or unsuitable for optical printing, and use conventional chemical processing, alternate chemical processing, or other non-traditional image development processing, such as that used in instant photography or applied heat without liquids.
According to the present invention, there is provided a solution to the problems of the prior art.
According to a feature of the present invention, there is provided a method of digital photofinishing comprising the steps of: producing a digital color image in printing or other densities of a color image captured on alternative capture photographic media; first mapping the printing or other densities of the alternative capture photographic media to the printing densities that would have been obtained for reference color photographic media; processing the mapped digital color image with a scene balance algorithm to produce a processed digital color image; second mapping the processed digital color image through a hard copy media characteristic curve to produce a mapped digital color image mapped to print densities of the hard copy media; sharpening the mapped digital color image with a sharpening algorithm optimized to avoid unacceptable artifacts; and digitally printing the sharpened digital color image onto hard copy media.
According to another feature of the present invention, there is provided a method of digital photofinishing comprising the steps of: producing a digital color negative image in optical or other printing densities of a color image captured on a color negative photographic element which is optimized for producing a color image suited for conversion to an electronic form and subsequent reconversion into a viewable form; mapping the printing densities of the digital color negative image to the printing densities that would have been obtained for the reference color negative photographic element; processing the mapped digital color negative image with an underexposure scene balance algorithm; mapping the processed digital color negative image through a hard copy media characteristic curve to produce a digital color positive image; sharpening the mapped digital color positive image with a sharpening algorithm optimized to avoid unacceptable artifacts; and digitally printing the sharpened digital color image onto hard copy media.
The invention has the following advantages.
1. A digital photofinishing system is provided that produces high quality digital photographic reflection prints from alternative color negative film images that match those that would have been obtained from a reference film at high print rates.
2. Sharpness that is difficult to correct in conventional optical photofinishing systems is corrected by digital image processing in a digital photofinisher.
3. Prints produced by the digital photofinishing system of the invention were preferred over prints produced by optical photofinishing systems.
4. Prints produced by the digital photofinishing system that have improved overall print contrast from color film negatives that are under-exposed.
5. Prints produced by the digital photofinishing system that have a preferred image contrast position relative to a traditional optical print.
6. The contrast normalization algorithm improves quality of low contrast scenes by increasing image contrast and of high contrast scenes by decreasing image contrast.
7. Improves quality of prints produced from low activity film and/or paper chemical processes by increasing the print contrast.
8. Improves quality of prints produced from high activity film and/or paper chemical processes by decreasing the print contrast.